Question: Harry took out a loan from the bank. The variable $D$ models Harry's remaining debt (in dollars) $t$ months after he took out the loan. $D=-200t+9000$ How much does Harry pay back each month? $\$$
Explanation: The rate of change of the equation is $-200$, which means Harry's remaining debt is decreasing by $\$200$ per month. This means Harry pays the bank back $\$200$ each month for his loans. Harry pays $\$200$ back each month.